I’ve seen capybara in the wild, and they are indeed fascinating and bizarre creatures. The phrase “gruffly wise” does indeed sum up their appearance quite well, though I would describe their vocalisations as being like those of a guinea pig rather than a Geiger counter, but perhaps I’ve never heard a twittering Geiger counter.
I’m not sure I approve totally of keeping a lone capybara as a pet because they are highly social animals, but he sounds as if he gets plenty of social contact from his humans to make up for it.